Safety plug for pressure cookers



Patented Dec. 25, QS

UNITED STATES T OFFICE SAFETY PLUG Foa PRESSURE cooKERs Myron J. Zimmer, Wood Dale, and Edmund L. Duskey, Western Springs, Ill., assignors to Ekco Products Company, Chicago, Ill., a corporation .of illinois 'I'he invention relates to safety plugs for limiting the pressure attained in a pressure cooker, particularly in a cooker of the type adapted for home use.

The general object of the invention is to provide a novel safety plug for a pressure cooker of the foregoing type, which operates either on excessive pressures or excessive temperatures.

Another object is to provide a novel safety plug fora pressure cooker, having two different forms of pressure releasing means, thus definitely insuring release of excessive pressure, should either of such means fail to act.

A further object is to provide a novel safety plug for a pressure cooker, which includes a release fundamentally dependent'r on temperature for its operation and a release dependent upon pressure alone.

Still another'object is to provide a novel safety plug for a pressure cooker, which combines two releasing means in a single assembly having a that food particles may lodge in the passagesV leading to such valves and render the valve inoperative, a safety plug is usually employed, such plug being mounted in the cover and being of a, character which cannot normally be rendered inoperable from contact with food in the receptacle.

Such safety plugs are usually of tWo forms, one

size substantially the same as that employed for a plug providing a single release.

A still further cbj ect is to provide a novel safety plug for a pressure cooker for home use, which includes a fusible metal release so mounted that it does not involve the customary threaded connection with the cover and can easily be replaced by the user merely by forcing it into the aperture in the cover provided therefor.

Other objects and advantages will become apparent from the following description takenin connection with the accompanying drawings, in which:

Figure 1 is a fragmentary vertical sectional view of a pressure cooker having a cover provided with a safety plug embodying the features of the invention and showing the cover of the cooker in closed position.

Fig. 2 is a fragmentary plan view of the cover of the pressure cooker and showing the plug in position therein.

Fig.,3 is an enlarged sectional view taken on the line 3-3 of Fig. 2 and showing certain parts of the plug exaggerated to illustrate a feature of the invention.

In pressure cookers of the type adapted for home use, a spring-operated pressure release is usually provided, which permits relief of the pressure in the cooker when the pressure therein reaches a predetermined value. The release device usually comprises some form of valve which is held seated by a spring and is adapted to be opened against the force of the spring by the pressure in the receptacle. Because of the fact comprising a resilient rubber disk retained in an aperture in the cover and adapted, when the pressure reaches a predetermined value above that for which the spring-operated valve is set, to become distorted and be forced or blown out of the aperture in the cover, thus relieving the pressure in the receptacle. The other form of plug frequently employed is of the fusible metal type, in which a small slug of fusible metal is mounted in a sleeve secured in an aperture in the cover. The fusible metal is of such character that it will soften at a temperature corresponding to the boiling point of water at a predetermined pressure. When such predetermined pressure and temperature are reached Within the receptacle, the

fusible metal softens sufficiently to be blown out of the sleeve in which it is mounted by the pressure within the receptacle and thus relieve the pressure therein. v y

Both types of safety plugs may, through an aging process or from misuse, be rendered inoperable to relieve the pressure at the desired value. Thus, the resilient rubber type of plug may, through age and constant subjection to high temperature, become so hard or so adherent to the metal of the cover that it cannot be forced through the aperture in the cover except by a pressure substantially higher than desired. The fusible metal may from misuse become so jammed in its mounting sleeve that it may not operate properly. It is true, of course, that the occasions when such diiculties arise are rare and under normal conditions either of these forms of safety plugs is sufcient. However, because of the great damage and injury that could result from permitting excessive pressures to be attained in a pressure cooker, it is of utmost desirability to insure operation of the safety plug under all circumstances.

The present invention provides a safety plug embodying the features of both of the former types and so combining them in a single structure that they may be easily handled in manufacture and inuse. Thus, we may provide a safety plug of the fusible metal type, in which a slug of fusible metal is mounted in a metallic sleeve located Within an aperture in the cover of the cooker;

The sleeve, of course, has to be sealed to the cover to prevent leakage therebetween and to be able The fusible metal on the otherhand is'p'rel'er-" ably of such character and isso mounted inits sleeve that it will be softened-suliciently to. be

forced out of the sleeve at a temperature Vcor-.-

responding to the boiling point of water at a different preuetermined pressure in thereceptacle.

Such safety plug is intended to be used in a cooker along with the spring-operated valve typelofM release so that there is provided, first, a springoperated. valve-,adapted to open at-onezpredeterf i mined pressure, the .resilient :sealing means yof.- the safety plug-adapted `to be forced out of the cover atasomewhat higher predetermined pressure,andthe fusiblemetaladapted to soften and be forced-out of its sleeve lat afstill higher `predetermined-pressure. rl'he invention, however, is notllimlted to lasafety plug-in whichuthe resilient sealing means is adaptedV to oereieased ata pres-v sure lower than the fusiblemetal plug. 'Ihearrangement may-be such .that the vfusible: metal. plug -is releasedat a-lower pressure than the resil-` ient sealing meansf To illustrate the invention, we have shownV in.. .f-

Fig. 1- of the drawings one type of pressure cooker,

but it is to `lne-understood, ofcourse, that our invention isfnot limited tothis particular type andV may-be used in'cookers of other types. YIn Fig.` 1 of the drawings; the receptacleis indicated at I0 and the coverat II. In this particular cooker, the receptacle -isfprovided-at-its top with an in- 'wardly turnedange I2 having an elliptical open-V ing ltherethrough, and the cover I I carries -a resilient gasket I3" adapted to engage-the under side -of the -ange I2 to seal-the receptacle The I cover II, in order to be removed, is adapted-ato be lowered; sufficiently to'move the gasket-l3-o1it of contact -vvith the flange I2 ahdthen 4to1 be f rotated 'through 90 so that the rshort diameter of thecover is aligned withl fthe long diameter of the 'opening through the -ange I2, and the covery may then be tipped to remove=itfromf the receptacle; VThe cover is supported by a bridge adapted to'be rotated by alknob I5'. 'The' knob 1 I5 is connected to the .cover II by means of a; stem I-S, and aspringH is interposed between i the bridge member I4 and the knob I5 tending' to lift the cover so that 'the gasket I3 is in sealingv engagement with the flange I2 ofthe receptacle. The bridge member I4 may be provided with af cup-shaped member 20 having interlocking means indicated `at 2|, with asleeve 22 mounted within the knob I5, so that the cover may be lockedV in a lowered position relative to the bridgernern` berA I4. Such locking means is .disclosed in the Myron J. Zimmer application Serial No.'598,725,

filed June 11, 1945, and now Patent No. 2,531,717,A

but forms no part of the present invention.

on the cover II.

mounted so that it .occupies a position` adjacent the bridge member I4 when the coveris in. sealing engagement with the receptacle. The cover, when turned by the knob I5 to move it out of alignment with the receptacle opening, of course carries the pressure release 23 with it and thus there is space between the two sides of the bridge member I4 for such turning movement of the pressure release without interference-z.;

Thel safety-plugembodying the features -of the invention is indicated in the drawings at 2d.

` Suchsafety plug, as heretofore mentioned, em-

known temperatures.. IBy using.: predetermined.'- proportions :of such metals,- vthe plug .2 mayibe 5.,

such that itwill A'operate at a1predeterminedtem-.-V

perature. In the present instance, such predeterfil mined temperature Yis that corresponuingnto, the

boiling point of waterzat a v.predeterminedilprese: A sure.V Thus,-the fusible metal-fplugwlllsor'ten sufficiently to be blownfout of the sleeve-25 at ai.

predetermined pressure Awithin. lthe receptacle I.-

In the prefer-red construction shownA iniaFig. 3,- the interior of the sleevev 25v is"tapere'd. as at 30 and' threads are-,cut in. the ata-per lso thatifull'` threads are formed at theilowersendinfthe .if

sleeve andthe threads` thereaboveware reducedv by' the taper to such. an extent. thatat the top lof the sleeve ino` threads' at: all appear.: Thesfusible metal, after beingplaced--insleeve A2:'5gisswaged so that part of the metal thereof is forcediintonx. the threads at the lower 'endr-of-ith'e sleeve 25bandV a portion thereof is inc-rel orless frivetedl'overlthe lowerendof the-sleeve i251, as indicated at SI. When the plug 21 softensfthe swagedfportion 3|` at the lower end of the Sleevecan be easily-dis#y i torted, under. :the pressure'within `the receptacle,V and :the iportionlof the '.fusiblelmetaliiforced .into Y the threads-.will ialsoebe distorted'so that-the-Lv plug will beA forcedlupwardly'throughthe sleeve; by the pressurepal -By the tapered character-of th-f threads :within the sleeve; upward movement-lof the plug therethrough-ismoreeasilyeifected the ff; farther. Aup the plugl' 21 is .'moved.` i: Thus;` once!V a pressureisuflicientto start'ftheplugi moving is attainedVthe plug will'b'e forced all the .way'rl through the sleeve and out of the top thereof Awithout `danger `off its becomingjammed. in4 the upper portionof theisleeve. f--This insures deniteloperation of:` the 'pressure vrelease at .the desired4 pressure:l 'While we haveshownfthe linterior of the sleeve 25 as being threaded, i-t.,is`,`.of.course, .i

obvious that any: other I form of roughening ofsuch interior wou-ldprovide the 'necessary a'ction; 11 However, threading of the sleeve Beal-simple;op-A

erationtol perform and,2;therefcre',fto facilitate. manufacture',.it is emplcyedsry ,f `As heretofore mentioned,.fusible-metal?safety f l plugs are usually mounted in the cover-nf' the receptacle with i a. s gasket.v r`of resilient f materialVV interposed- "-betweenthe `.=metal y sleeve i and4 the cover.; so that"a1deiniteseal willf'be effected.:

therebetween..` In the present/instance, .a resil-1-V ientzseal is interposed-between Ythe sleeve 25fan'd` .s Y the `cover VI I, but such seal is soformed that'itfis c given the additional.functionof constituting in :f itselffafpressure release, such releaseoccurring== at ,a 4 pressure differing from that underwhich and grease, such as the synthetic material known as neoprene The disk 32 in its preferred form is provided with an upper flange 33 which overlaps the mar-Y ginal portion of the cover about the aperture 26 only sufficiently to permit the plug 32 to be retained therein under ordinary handling. The flange 33 is preferably made as small as possible so that the plug 32 may be inserted in the aperture 26 from the inside of the cover II without having to distort the plug 32 to any great extent. The plug 32 also includes a lower flange portion 34 which engages the under surface of the cover Ii about the aperture 26 and provides the desired seal. The two flanges 33 and 34 thus provide a peripheral groove 35 in the disk 32 in which the edge of the cover II is seated, the root diameter of the groove being such that the plug snugly engages the edge of the metal. Under normal pressures within the receptacle, the flange portion 34 is forced against the under face of the cover II and effects a seal therewith, the pressure thereby maintaining the desired sealing relation. However, when the pressure exceeds a predetermined value, such pressure will disto-rt the flange portion 34 and the material ad-V material and in a given mold will operate at substantially the same value. To confine the distortion necessary for release of the disk memberk 32 from the cover, the central aperture in the disk 32 in which the. sleeve 25 is positioned is countersunk as at 36.to provide a shoulder 31 which lies in substantially the same plane as the under surface of the cover I I adjacent the opening 25. The sleeve 25 is provided with a flange 40 at its lower end fitting within the countersunk end 36 of the disk 32 in engagement with the shoulder 31. The pressure in the receptacle, of course, is applied to the inner end of the sleeve 25 and the plug 21, in addition to being applied to the inner face of the disk 32. Force due to such pressure exerted on the plug 21 and sleeve 25 is transmitted through the flange 4l) to the shoulder 31. Since such force is exerted on the disk 32 in the same plane with the lower face of the cover II, the material of the disk 32 within the aperture 23 and thereabove does not have to be distorted in order to be forced through the aperture 25. Only the flange portion 34 and the material immediately adjacent thereto need be distorted, so that uniform operation of disks of this characteris thereby obtained. The upper end of the sleeve 25 is also provided with a small flange or bead 4I sufficient to retain the sleeve Within the disk 32. The bead 4I is preferably rounded so as to facilitate insertion of the sleevek 25 into the disk 32 from the inner face thereof. the disk 32 having a snug t about the main body, of thesleeve 25. Y

The combining of the two safety releases into one assembly has an added feature when the various parts of the cover are considered. The cover, as will be noted, is centrally apertured as at 42 for the stem I6.` At .the left side of the cover, as shown in Fig. l, the cover is also apertured at 43 for the spring-operated pressure release 23. The safety plug 24 is preferably mounted under the bridge member I4 so that when either the disk 32 is blown out of the aperture 23 or the fusible metal plug 21 is blown out of the sleeve, 'they will strike the bridge member I4 instead of being blown at some distant point in the room or into the face of the person using the cooker. The bridge member I4 thus serves as a guard when either of these parts is blown out of the cover. With such positioning of the safety plug 24, the aperture 23 is generally aligned with the apertures 42 and 43. If

the fusible metal plug and resilient disk 32v were mounted separately in the cover, this would involve still another aperture in such line and there would result a general weakening of the cover along that line.

The total forces involved are rather substantial. Thus, assuming that the spring-operated release 23 is set for l5 pounds and assuming the area 0f the cover Il is approximately 30 square inches, the total force on the cover when this pressure is attained is in the neighborhood of 450 pounds. Assuming that the disk 32` is constructed to release at a pressure of 25 pounds per square inch, the total force on the cover is then in the neighborhood of 750` pounds. If the fusible metal plug 21 is adapted to be released at a pressure of, say, 35 pounds per square inch, the total pressure on the cover is in the neighborhood of 1050 pounds. It is evident from these figures that the force exerted on the cover is relatively large so that any weakening of the cover might result in distortion thereof under such pressure. Any distortion of the cover cannot be tolerated, of course, because it would tend to produce leakage of pressure between the gasket I3 and the flange I2 of the receptacle. By combining both the fusible metal plug 21 and the resilient disk 32 into one structure, one aperture through the cover is eliminated so that the cover will not thereby be weakened to any substantial extent.

The inclusion of a fusible metal release as a part of the present plug provides a feature inherent in the use of such metal. For example, should a slight leak develop in or about the cover, the desired pressure in the receptacle may not be obtained but the water placed in the receptacle or included in the food therein will be permitted to boil away, leaving the receptacle dry. Under such circumstance, continued application of heat to the cooker would, of course, burn the food by causing an excessively high temperature within the receptacle. Such condition would not be readily detected except by the odor resulting therefrom. rIhe fusible metal, however, will soften at a predetermined ternperature, even though no great amount of pressure'is present. The fusible slugr 21 will, therefore, soften and may drop into -the receptacle to open the sleeve 25. The odor of the over heated food can then pass out through the sleeve and'will be readily detected before the receptacle is damaged by excessive heat.

Fromfthe aforegoingg fit. is; apparent. V:that awe r and shaving'fazsiiangeportiom adaptedto;1 engage havagprovided ainovelxsafetyzuplug for ..ai;pres..

sure cooker, in which two releasingmea-nsare providedeixThe yrubber disk 32. willwberleleased as aeresult of'pressure along.

Thefusible finetal,

iv turersaid disk having -ascentral .aperture counter-J sunk `ateitsA inner) end `to provide a Vshoulderlying` in substantiallyVV the same-.plane-J asv the cover-1...

however, will-libe' releasedmeither@underthe in e uence-pi :the 4temperature .corresponding to; vthe boiling point of '.watenlattained underea prede-- termined pressure. or: will fbe released lunderthe attainmentsof. an `excessivetemperature alone without excessive pressure,

We claim:;

1.1A.pressure relief :plug for apressure-cooker.:

comprising,y a resilient .diskmember .adapted t etc.

be placed. in` an aperture in the v.cover ofthe cooker;;and1having a peripheral: groove. .adapted to receive the .marginalxportion of: saidcover about lsaid. aperture, said '.diski.' having ra lcentral-1:1.: boraasleevesecuredin said bore,4 andaiusiblefi.-

membermOunted in said sleeve, said- Adiskbeing adapted to be forced out of said apertureat a.

predeterminedpressure insaidcookeriand said .l fusible .members` being .adapted to be softened suciently: to be forced out of saidvsleeve vat a temperature corresponding' to a diierent v prede\ termined pressure;u

2. A pressure relief plug for vthe cover-oi?- a pressure cooker,- comprising a metal-sleeve, 1 a fusible metal plugl mounted in.v saidf'sleeveA-and adapted .to be released by softening at a tem-- g in an aperture in the cover, afusible metal plug perature correspondingto a predetermined pressure, and aresilient rubber diskhaving a central the inner surfacefof the coverilabout.saideaper engaging. surfaceoiusaidiflange portion, a. metaLv sleevettingsnugly in said central aperture and having a.. flange .fitting in the :countersunk .end

thereof in.A abutment with.. said: shoulder, .andra fusible imetalr-plug.imountedlin said sleeve,` the l pressure .on-said. sleeve .land .plugbeingapplied .to

said shoulder whereby, when said disk .is-.forced out ofthe aperturefbyu pressure, only the portion.

of said-diskadjacen-t to and including saidnange.

port-ionrneed be distorted..

permit release ofsaid means. throughsaid aperturen,V i

. 7. Ai pressure -reliefplug for a pressure cooker;V

comprising va metal sleeve adapted tobe located mounted insaid sleeve, and-an annular. resilient rubber .member interposed...between.said.sleeve` andthe 'cover to provide a seal therebetween and. beingldistortableunder pressure. to. permit it toV s be forced through saidlaperture.'

aperture in which-saidsleeve is. mounted, said disk'being'fadapted Ato bepositionedin an aperture in the cover'with a peripheralgroove inthe diskto receive the marginal `portion or Athe cover about said cover aperture.

3. A pressure relief plug for the cover of a pressure cooker,v vcomprising a centrally vaperA tured resilientlrubberI supporting disk-adapted to be 'placedlin-an aperture `in the coverfoi. the

8. Alpressure relief plugior a` pressure cooker, Y comprising.asupportingmem'ber adapted .tobe located in an. aperture insthe .cover of the cocker.

and having a tapered bore with its smaller diame.. ter 4at its inner or lower end,Y f Asaid .borev being threaded with constant diameter. threads. whereby the depth of the threads decreases toward the top of the bore; and a .fusible` metal plug mounted inV A the lower end of the bore andswaged to enter the cooker and having peripheral :flanges fadap-ted to engage opposite Vfaces of the cover about said cover aperture, a metal sleeve .mountediin and extending through .the Ycentral aperture in said disk-and having iiangeportions at opposite ends engaging the faces ofthe disk to holdl the sleeve threads 4atsaid `lower end, the .decreasein depth of the threads toward Ithe top of the boreifacilitating release ofthe plug when softenedand forced outwardlyby. pressure in the cooker. .1

9.' A pressure .relief plug for a pressure cooker;

` comprising asupporting member adapted to be within thevdiskaperture, and-a. fusible metal plug mounted in said sleeve and adapted to be released by softening at aV temperature corre--f sponding to a predetermined.pressure@ s located in -an aperture in the cover oi the cooker u andfhaving a tapered bore with its'smaller diame- 4. A` pressure relief plugfor the cover ofa pressure cooker, comprising a centrally aperturedI resilient: rubber supporting disk adapted. .to be placedv inan aperture the coveroi the cooker and.havingperipheral-hanger; adaptedto engage opposite faces of the cover aboutr said cover ener- A ture, a metal sleeve. mountedzinA and4 extending through the centrallaperture in said diskand having flange portions at opposite ends engaging the faces of the disk'to hold. the sleevewithin the 1- disk aperture, and a fusible metal vplug mounted in said sleeve and `adaptedtobe released by softening at a temperature corresponding toa pref determined pressure,v the outer flange onthe diski.

being only sufiicientin size to prevent dislodgement ofthe plug inhandling the cover-.and the .7.

inner flange on the disk being suiiicie-nt. in size. to hold the plug in. place up to a predetermined pressure, the iiange-.portion Aon the outer endfof said sleeve being roundedin form to facilitate insertionof the sleeve through said disk. n

5.` A-pressme relier pluggfor al pressure cooker,.

comprising `a resilient rubberfdiskadapted tobe inserted in an aperture inthe cQvenoithe-cooker..

ter at its inner or lower end,said bore having grooves-vof. constantroot. diameter whereby the depthpf the groovesndecreases'toward the `top of thebore,y and a fusible metal plug mounted in the -borewiththe metal of the plugformed into said` grooves, the decrease in depth'of the grooves t toward the top of .the bore facilitating release of..

the plug when softened'and forced outwardly .by pressure in the cooker.; y

10. A'pressure relief plug for a vpressure cooker,

,Y comprising asupporting member adapted to ybe located in an aperture inthe cover. of the cooker v and :having la bore extendingtherethrough, and

' a fusiblemetal-y plug mounted insaid bore-theV surface of-said bore being transverselygroughened to providev inward .projections separated by deinto saidsdepressions to hold the plug against movement .in the bore, the diameter of said profv jections-increasing toward the top .or outer endVv of said bore to facilitate release of the plug when softened-and forced outwardly-*by pressure in the cooker.A

11. A pressure relief-plugfor a .pressure cooker,

Y comprisingfa centrally apertured resilient `rubber disk: adapted to. be; placed an aperture fin. the i pressions and the metal offthe plug being formedA i 9 10 cover of the cooker and having peripheral anges UNITED STATES PATENTS adapted to engage opposite faces of the cover Number Name Date about said aperture, and a metal plug located 670 794 Lott Mar 26 1901 in the central aperture of said disk and movl 142902 McNLt't'" June'15 1915 lable yaxially of said disk by a predetermined pres- 5 1750335 Taylor Mar 11' 1930 sure in the cooker to release the pressure. 2173999 GrundStrB-n: Sept' 26 1939 MYRON J- ZIMMER 2,224,296 Holman Dec, 1o, 1940 EDMUND I+ DUSKEY' 2,301,724 Vischer, Jr. Nov. 10. 1942 REFERENCES CITED 10 The following references are of record in the le of this patent: 

